Most of the world's supply of uranium currently comes from the mines.

Currently uranium comes from mines (deposits on land) and fetches say $100 per pound.
Uranium can be extracted from sea water but that is expensive (say cost of extracting one pound is $150) . So this method is not commercially viable.

Conclusion: If the cost of extracting uranium from seawater is not reduced, this method will remain commercially non - viable.

Since in case of seawater method, cost > price uranium fetches, the method is not viable.
What can make the method viable? Either cost of extraction reduces (to below $100 per pound) or price of uranium in the market increases (to above $150 per pound)
The conclusion says that cost of extraction must reduce. What will help us in evaluating it? What will help us find whether the conclusion makes sense i.e. whether cost must reduce to make it viable? We must find out whether price can increase to above $150 or not.
If price in market will remain at $100, then cost of extraction must come below $100 to make it viable.
If price in the market increases substantially, the cost of extraction may not have to reduce and it may still become viable.

(A) Whether the uranium in deposits on land is rapidly being depleted

If uranium on land is depleting rapidly, then price of uranium is likely to increase rapidly in the future and the seawater method may become viable.
If land deposits are huge and many, then price of uranium is likely to stay steady in the future and to make seawater method viable, cost of extraction must reduce. Hence, this option will help us in evaluating whether cost must reduce to make the method viable.

(B) Whether most uranium is used near where it is mined

Where uranium is used is irrelevant.

(C) Whether there are any technological advances that show promise of reducing the costs of extracting uranium from seawater

We need to find whether we need to reduce cost of extraction from seawater. Whether we have any promises tech to do that currently or not is irrelevant.

(D) Whether the total amount of Uranium in seawater is significantly greater than the total amount of uranium on land

The comparison of amount of uranium in seawater vs that on land is out of scope for us. We are discussing cost of extraction vs price in the market.

(E) Whether uranium can be extracted from freshwater at a cost similar to the cost of extracting it from seawater

Freshwater is out of scope.

Answer (A)

Hi

What if for option (b), even if the cost of extraction comes down but the cost of transportation from seawater site is more than that for the mine site, then would it not be necessary to evaluate option b??